SENSORY WATER QUALITY TESTING. Mike Wallace, Chief Public Analyst

Transcription

1 SENSORY WATER QUALITY TESTING By Mike Wallace, Chief Public Analyst ENVIRONMENTAL MONITORING AND RISK ASSESSMENT DIVISION Freeport, Grand Bahama ABSTRACT Reports, comments, and complaints to the Department of Environmental Health Services indicate that providers of public supplies of water, via piping, are having difficulty convincing consumers, and potential consumers, that the water is safe, and acceptable for drinking. Consumers use piped water for cleaning, and for cooking, but not for drinking without point-of-use treatment. The reasons given indicate that the concerns emanate from suspicions that utility companies do not provide constant care, and attention, to process norms; that the prevalent treatment with chlorine, exacerbates the situation by adding an hazardous reagent; and that the taste of the water varies, and is not as good as bottled water. The latter quality trait needs to be addressed, and it speaks to a need to appreciate the sensory quality of drinking water. Persons naturally engage in water quality assessment each day, when they drink water. Efforts to ensure water quality must, of necessity, include concerns over the level of satisfaction by consumers, as expressed in sensory terms. Sensory quality takes into consideration those constituents of water that influence foretaste, aftertaste, and smell. These tend to be due to trace levels of chemical substances, especially organics. This paper details the use of blind taste testing as one means to differentiate sensory quality through preference testing. This work is a preliminary assessment of water quality, and needs to be supplemented/complemented with a rigorous programme of collection of sensory information, and test data, to establish allowable, and achievable, post-treatment limits. KEY TERMS: Sensory acuity, sensory quality, foretaste, aftertaste, water quality, contaminants, Secondary Maximum Contaminant Levels (SMCLs), water quality), 6-Sigma Statistical Quality Control, Likability Testing, (a.k.a. Taste Rating Test), leachate, contaminant, odor, drinking water INTRODUCTION Objectionable taste and odor can more likely be found at the source (raw water) than at the consumer s tap. Earthy-musty odors are normally derived from natural biological processes. They can be classified as organic compounds, but there are also synthetic compounds of agricultural and/or industrial origin. John DeZuane in Handbook of Drinking Water Quality The thrust of Analytical Chemistry, and Microbiology, has been to identify species, and concentration levels of these species, that compromise the safety of water. We then designate that water with no/low levels of the problem species as safe, and when the levels are consistently low, we say the water is of good quality. In these ways, we relate to the World Health Organization (WHO) Guidelines (8) that define quality water (a.k.a. safe water), as containing mineral elements, in consistently low levels; and very low, and none detected, levels of microorganisms. 1

2 Bahamas potable water is abstracted from shallow groundwater lenses, stored in metal tanks, subjected to chlorine treatment, and is transferred via networks of underground piping of various materials. The risks for variations in (trace) levels of chemical, and microbial species, is represented in Table 1, below. For sensory quality, the keys include the sensory acuity of the individual consumer, and the variability of water, because the discerning palate will detect inconsistency, and when this happens, the utility will lose customers! Variations in Bahamas municipal utilities are attributable to seasonal modalities in, rainfall, and heaviness of rainfall intensity of dry/drought periods and, the relative concentrations of organics in abstracted groundwater due to the previous, (listed), factors, and, followed by the reactions of these organic substances with chlorine. There has been a dramatic, and continuing, growth of the Bahamas, and regional, bottled water business, because, 1. the product tends have a more consistent taste than piped water, 2. the bottle has become to be the symbol of superior quality, compared to piped water, 3. bottlers have better marketing techniques than utilities, and, 4. bottlers have successfully exploited the current ecological sensitivity when they point to residual chemicals in piped water, - especially chlorine, and its derivatives, - as being a public health risk to consumers; and,. do not offer that bottlers use oxidants, such as ozone. Sensory quality assessment is a means for utilities to establish a common yardstick for quality, once the Chemistry and Microbiology, are within (6-Sigma ranges of) Statistical Control Limits. METHODOLOGY A Preference Paired Comparison test method used for the trials as described in the Methods for Sensory Evaluation of Food, including the statistical assessment procedure described (1, 2, 6). The sensory test questionnaire was a modified version of one from the Samples of Sensory Test Questionnaires, one used for likability Rating Two of More Samples (6). Three (3) types of water were selected, two (2) local, bottled products, and a Freeport city supply, taken from the tap in the EMRAD office kitchen. All samples were used to fill Sunny Isles bottles, in groups of three (3). 2

3 All samples were chilled in the kitchen refrigerator. Once the panelists were selected for a blind tasting preferential test session, then the required numbers of bottles were removed from the refrigerator, and the panelists were asked to test the samples, giving first impressions. The panelists were volunteers, taken from groups of students and teachers from local secondary schools, and from a group of local journalists. Instruction sheets were provided, and these were explained prior to the tests. A pre-printed score sheet was provided for each panelist to use to apply scores to the samples, with no comparison of scores between panelists. RESULTS The scores were tabulated, as follows, along with descriptive terms, Type of water Score average (the lower the score, the higher the preference rating; scores were I, 2, or 3) Locally produced bottled Freeport city tap water Another locally produced water bottled water Standard Deviation in scores +/ / / (+/-) Variance in scores Comments from panelists Smooth, no aftertaste No taste Sweet taste Peculiar taste, no sodium Soft Thirst quenching Bitter taste Aftertaste Good, no taste Good, cool, refreshing Slightly salty Unpleasant aftertaste Very fresh taste Rough taste Like regular tap water Tastes like tap water Little salty Aftertaste Seems hard Funny taste Slightly sharp Moderate-strong aftertaste Tastes furry Soft Did not taste good Tastes awful Bad taste Aftertaste Heavier Tasted clean Tasted not good Traditionally, malodor, and microbial contamination, have been the concern for surface sources of drinking water, until groundwater contamination from landfills, industrial activities, and farm operations have become so prevalent. Now, shallow aquifers, as occur in the Bahamas, are particularly vulnerability to surface contamination, through leaching through rock/soil pores, and through rock fissures; and information now supports that coliform bacteria are able to persist in soil for extended periods, allowing leaching into shallow aquifers (9, 10, 11). The chemical species that cause taste, and smell aberrations in water include metal complexes at parts per billion levels, organics at parts per billion, (e.g. 1Ug/L for geosmin or methylisoborneol), and at parts per million levels, e.g. 20 mg/l for chloroform)(3). Some of these chemical species are referred to as Secondary Maximum Contaminant Levels (SMCLs), by the United States Environmental Protection Agency (EPA), and are contaminants of industrial, and agricultural, origin. 3

4 Utility providers need to work to anticipate, detect, avoid, minimize, and/or control levels of these malodor, and off-taste, species in water (10, 11, 12). Actions will involve the protection of watershed areas; the improvements of all area, and regional, waste management practices, particularly the use of disposal wells; and the establishment, and maintenance of groundwater monitoring programs. Equally, bottle water providers use the same water for their raw materials, need to be aware of these species, and need to work to minimize, or eliminate, them. The sensory evaluation tests on locally produced bottled water does show a significant frequency when off-tastes can be detected. CONCLUSIONS From this exercise, we list the following: 1. The comments listed were as the panelists expressed them, and these reflect a diverse assessment of each sample, supporting that sensory acuity, and what satisfies, are private, and personal, items. This raises the need for utility companies to maintain close contact with consumers, and, especially so to respond to customer complaints when these relate to subjective aspects of water. A. C. Nielsen Company has reported that fewer than ten (10) percent of consumers who have reason to complain about product quality defect do so, through writing to the manufacturer or distributor, (35 % returned the goods to the store where purchases were made),.. most of the others change to alternative sources for satisfaction (4). 2. The differences in scores for the twenty five (25) panelists, is not statistically significant. For each sample, some liked, some disliked, and some were ambivalent. This is the nature of the consumer, and the successful utility will review the comments, and build/engineer a market profile aimed at minimizing those who dislike, or are ambivalent,. Thus increasing market share. 3. The scores indicate personal bias of taste, but that there is little difference between the satisfaction achieved from using the products. This, given, the successful utility will look to additional means to cause satisfaction, - reduce product variability, community activism, education programmes, etc. to increase market share. 4. It is to be noted that the Freeport City water sample is rated highly in comparison with the popular, bottled water lots. The panelists rate the city water as equally satisfying as one lot, and more highly satisfying than the other. At the end of the each session, panelists were provided with the identity of the Freeport supply, and the general reply was that they never thought that tap water could be as good, as satisfying, as bottled water, showing that the selection of bottled water is becoming/has become, a cultural standard, rather than an outcome of objective assessment, and choice. 4

5 5. Successful taste, and odor, controls can be effected through in-field water treatment through 5.1 Effective monitoring, control, and management, over catchment areas/watersheds to minimize soil, ground, and groundwater, contamination (11, 12). 5.2 Effective application of vegetative cover to provide lowered porosity to leaching, and maximizes surface accumulation of contaminants, e.g. through use of cover grass on recharge areas. 5.3 And, through use of water filtration, as pre-treatment, and the use of filters sand, and finely divided activated carbon, to remove contaminants. Each of the five (5) items above serves to offer areas for action for utility providers to provide for increased market share, and to introduce sensory testing/organoleptic testing as an integral part of quality control testing. REFERENCES 1. Special edition on Sensory Evaluation, Food Technology, Nov 1973, The Institute of Food technologists. 2. Special edition on Sensory Evaluation, - Food Technology, November, 1976, The Institute of Food Technologists. 3. William H. Bruvold, (1992), Sensory Research for the Establishment of Secondary Maximum Contaminant Levels, Water Resources Bulletin, August The New Silent Majority, an A. C. Nielsen Company Study of Consumer Attitudes towards Quality Defects, Hirsh, Naomi L., (1975), What Type of Test and When, Samples of Sensory Test Questionnaires, Sensory Evaluation Division Symposium, Institute of Food Technologists National Convention, June Canada Department of Agriculture, (1970), Methods for Sensory Evaluation of Food, Publication DeZuane, John, (1990), Handbook of Drinking Water Quality, 2 nd edition, John Wiley & Sons, Inc. 8. World Health Organization, (1993), Guidelines for drinking-water quality second edition, Volume 1 Recommendations. 5

6 9. Hunter, C., et al, (1991), The Occurrence of Coliform Bacteria in the Surface Soils of Two Catchment Areas in the Yorkshire Dales, Journal of the Institution of Water and Environmental Management, Vol. 5 No. 5, Cheremisinoff, Paul N., et al (1984), Groundwater Leachate, Modeling, Monitoring, Sampling, Technomic Publishing Company, Inc Wilkes University Center for Environmental Quality GeoEnvironmental Science and Engineering Department Monroe County Outreach Program: 11.1 Monroe County Groundwater Monitoring and Testing Program ( Drinking Water Tastes and Odor Problems ( 12. Russell, David L. (1987), Understanding Groundwater Monitoring, Chemical Engineering, October 26, 1987 TABLE 1 - FACTORS OF VARIABILITY IN BAHAMIAN WATER QUALITY The occurrence, handling, and presentation, of Bahamian piped water, has the following consequences: SITUATION Water occurs in a dynamic equilibrium with saline water, separated due to differences in specific gravity Water is in intimate contact with limestone Water is impacted by leachate from rotting organic matter Water is impacted by underground contaminants, - bacteria, organics, and minerals, - aided by fissures associated with root zones of natural vegetation, and the burrowing actions of earth dwellers Water is impacted by microbial species, where microphages/macrophages vary according to soil/rock depth, and soil/rock aeration; and where the microbes have varying efficacy for fermentation based on varying levels of aerobic/anaerobic conditions in soil Treated water is conducted to consumers by way of underground pipelines, composed of different substances; and, significant quantities of water are not accounted for, with indication that leaks occur in piping MANIFESTATION Water is of variable levels of salinity Water contains differential levels of dissolved minerals from limestone residues Water contains differential levels of dissolved organic matter, made more different due to differing intensity, and duration of rain showers, and permeability of rock/soil media Water contains differential levels of contaminants and minerals Water contains differential levels of microbial species, microphages, and macrophages; and varying levels of gases Water contains trace levels of a range of impurities from piping materials, and from ground species. 6